In the field of biotechnology, there has been known a method in which using an antibody labeled with an organic phosphor, a phosphorescence emitted upon exposure to ultraviolet rays is measured by an optical microscope or a photodetector; in fact, however, such a method exhibits low sensitivity and is rarely applicable for quantitative measurements. This is due to the fact that an organic phosphor exhibits a low emission efficiency and is also destroyed upon exposure to electron beams.
On the contrary, inorganic phosphors are stable and rarely deteriorate upon exposure to ultraviolet rays or electron beams. Inorganic phosphors are practically used for displays and lamps but these phosphors, which are generally not less than 1 μm in their particle size, are not practical for use as a phosphor for molecular labeling.
An inorganic phosphor used for a phosphor for molecular labeling requires not only reduced particle size but also adsorption or bonding of molecular-labeling substances such as proteins or DNA is also required. Surface physical properties of an inorganic phosphor vary adsorbability or bonding capability. To control surface physical properties, there were proposed methods for surface coverage (as described in, for example, Patent document 1), but produced problems such that a surface-covering compound inhibited adsorption or bonding of a molecular-labeling substance, or the surface-covering compound absorbing excitation light resulted in reduced emission efficiency.    Patent document 1: JP-A No. 9-291273 (hereinafter, the term PP-A refers to Japanese Patent Application Publication)